I'm 40 and trees are tuff but as times gone on the job has gotten easier and I've got harder. Office job people don't get it the guys my age are soft and weak. No thanks I made the right call. When I'm older I can just run 1 machine it's no work at all. Mini skid- grapple loader truck are not hard work. I have no joint pain and blood pressure that may b too low in great shape for age and size.
Working smarter, not harder!
Older tree guys do have a rep for being all worn out- but it's mostly because of other poor life choices they've made, especially substance abuse
My guy who grind stumps still occasionally climbs for us at the ripe age of 63. His technique is very old school but is actually faster than most climbers I know and doesn't seem to have any health issues.
I've also worked with Beastmaster here on AS when I lived in Cali. Great climber and healthy lifestyle now in his mid sixties.